For ease of moving from one work site to another, it is often preferred to use a relatively light lift and rely primarily on retractable or removable outriggers for stability rather than relying on the weight and weight distribution of the lift structures for stability. Typical portable lifts with outriggers are shown in U.S. Pat. Nos. 4,015,686; 4,458,785 and 5,121,816, for example. As shown in the latest of these patents, it is preferred to provide a safety system which does not permit the work platform to be raised unless the outriggers are in proper supporting position.
There is also a need in portable weighted lifts of the type which can be moved on the work site on wheels and/or casters to provide a safety system to disable the system for raising the work platform whenever the support base for the lift is not level or does not have stable ground support adjacent its four corners.